When you say run y axis and a axis in tandem do you mean you have a 4th rotary axis (for cutting pipe) or just have 2 motors on the gantry that you need to move together?
For the first see my comment above......
For the second
Make a new config, select your "a axis" as tandem Y.
You will need homing switches on each of the 2 y axis so the joints can square themselves before becoming an axis. Once they are homed both will move at the same time and jog like normal.
